This invention relates to devices for regulating the pressure of a fluid within a fluidtight vessel or other fluidtight apparatus and more especially for avoiding, or at least reducing, pressure differences between the inside of the apparatus and the surrounding ambient medium. The term "fluid" as used herein means any liquids, greases, and pasty materials.
More specifically, it relates to devices for use on apparatus exposed to an ambient medium at high pressure and elevated temperature and especially (though not exclusively) when it is subject under such conditions to temperature and/or pressure cycling.
An important application of the invention is to fluid-filled electric connectors and other apparatus for subterranean use in an oil well.
Under such conditions, the integrity of sealing of the apparatus is liable to be at risk, and the most acceptable way of avoiding leakage is usually to maintain the seal(s) pressure-free or nearly so, and this entails provision for accommodating changes in the volume of fluid as temperature and/or pressure change. Sliding pistons are unsatisfactory when the ambient medium contains particles that are liable to be caught between the sliding surfaces, and simple bellows arrangements are liable to fatigue failure or the like.